Control Moment Gyroscope Notes

Below is a picture of a full-scale mockup the Control Moment Gyroscopes (CMG's) as they'll be mounted on the International Space Station. Some notes:

1. The two large black circles you see on each CMG are not part of the flight configuration. Those are holes cut in the WETF mockups to let water through.

2. Note the box on the CMG at the lower right. That is the Electronics Assembly, a removable avionics box containing all the electronics associated with control and data collection for that CMG. Each CMG has its own EA box. Note that they do not appear to be in the same position on all four. That's because the CMG's are actually mounted in four different orientations.

3. The CMG's are mounted diagonally, but only because Rocketdyne had to tilt them over to fit them all onto the Z1 truss. These CMG's were originally designed to go on the S2 truss, where they mounted in a similar cluster but oriented in alignment with the space station's Z axis. The mounting angle doesn't really matter since the actual gyroscopes are free to rotate every which way inside the CMG housing.

4. Scale references: The CMG's are 48 inches in diameter. The parabolic antenna at the top of the Z1 truss is 72 inches in diameter. That is the space station's main Ku-band antenna. (Actually, the mockup is a Radio Shack TVRO antenna, from the local Radio Shack at Baybrook Mall in Houston.) These four CMG's have sufficient control authority to control the attitude of a half-million-pound space station, so something this big would be overkill on the Reference Mission spacecraft or assembly node.

5. The silvery box to the left of the CMG's is an EVA tool box.

6. The gray thing the CMG's are bolted to is mockup of the Z1 truss. This unit is a kludge, replacing the functions of the old S2 segment. The Z1 truss exsits because of a commumnication problem between NASA and the Russian Space Agency. NASA thought the Russians' FGB module would be able to provide control for the whole space station, but the Russians meant that it could control the Russian elements. The FGB also cannot provide the Nav Base functions or power requirements of the whole space station. When NASA and RSA finally got that communication across, it was clear that the U.S. elements would have to provide those functions. Rather than bring back the S2 segment, NASA decided to add the Z1.

7. Everything you see is a WETF mockup. The Ku-band antenna and the CMG's were built for one of my tests, the S2 Phase 1 WETF test, conducted in Feb 92 at the JSC WETF. Rocketdyne built the Z1 mockup structure. The mockup was tested as shown in this picture at the Neutral Buoyancy Simulator at the Marshall Space Flight Center in Huntsville, Alabama.

8. Each CMG has a mounting ring, sort of a belly band, that bolts in six places to space station primary structure. You can see the little tabs on the ends of the mounting rings. The two tabs next to the axis of each CMG might not be so noticeable. The mounting rings on the real CMG's are more distinct; the mockups' mouting rings were just molded as part of a single unit along with the rest of the housing. The mockup housings are made from vacuum-formed plastic. The real CMG's will be covered with multi-layer insulation, so their texture will look quite a bit like the mockups in the photo.

9. There are handholds on the mounting rings, to aid the crew in handling the CMG's.

10. The black holes in the Electronics Assembly are mockup-specific.

11. Trunnion pins and scuff plates are visible on the right side of the Z1 truss.

12. All those yellow things are EVA handrails.

13. Photo credit goes to NASA, I think; it might be a Rocketdayne photo.